Dietary supplements containing viable probiotic bacteria are increasing in popularity in the marketplace as their health benefits become recognized. These benefits, in addition to supporting intestinal health and function, include (depending on the bacterial strain selected) repopulating the gut after antibiotic therapy, offsetting lactose intolerance, supporting the immune system and reducing cholesterol. Lactic acid bacteria, primarily from the Lactobacillus and Bifidobacterium genera, that are capable of improving or maintaining intestinal health and function are termed probiotic bacteria. Probiotic bacteria (referred to herein as probiotics) are sensitive to various environmental conditions such as pH, moisture, temperature, air and light. When these conditions are not properly controlled, the product's viability (measured in colony forming units or cfu), and therefore its efficacy, can be substantially reduced. Products with reduced viability and efficacy have been commercialized, which has contributed to probiotics as a class not achieving the same level of market acceptance as other health supplements.
New generation strains that adhere to intestinal epithelial cells and persist longer in the intestinal tract have appeared in the marketplace in the last few years; these strains are more efficacious compared to strains previously in use (old generation strains). Probiotic companies have isolated new generation strains directly from the intestinal tracts of healthy people rather than from cultured dairy products or other foods, which were common sources for old generation strains. These new, human origin strains are often more sensitive to processing conditions, such as fermentation, concentration and drying and, thus, require special handling in order to survive commercial preparation. Conventional processing techniques, developed largely for old generation strains, are often too harsh for these new generation strains.
Both new and old generation probiotic stains are sensitive to water activity (aw or aw), should be in a dry formulation, and to the low pH levels commonly encountered in gastric juice. A high water activity reduces product shelf-life while low pH will reduce cfus and thereby decrease product efficacy. Exposure of both new and old strains to gastric juice at pH 1.5–2.0 for 90 minutes caused reductions in cfu exceeding 99.99% (see Example 1 below). Thus, when dietary supplements containing these strains are administered in conventional capsules or tablets which degrade quickly in the stomach, most of the probiotic bacteria are killed in the stomach before they reach the intestinal tract, which is where they are expected to exert their beneficial effect. Many probiotic manufacturers recommend a substantial daily dose of 1–20 billion cfu which, apparently, is high enough to compensate for the loss experienced in gastric juice. But such a high overage in dosage adds significant cost and negatively affects marketability.
Water activity (aw) has a direct effect on the shelf-life of probiotic products. Values of aw of 0.07 or higher can dramatically decrease the shelf-life of probiotics. U.S. Pat. Nos. 4,956,295 and 4,927,763 disclose that when dry probiotic bacteria are blended in certain carriers such as inorganic salts (that adsorb less than 1% water by weight) along with 1 to 5% silica gel or 0.1 to 2% molecular sieve adsorbent, the resulting mixtures have an aw in the range below 0.30, such as 0.10 to 0.25. To maintain shelf-life, attempts to protect probiotics from pH sensitivity must also take into consideration the aw of the resulting formulation.
Past attempts to correct the pH sensitivity of probiotics by employing microencapsulation or enteric coating techniques have generally not proved to be protective from pH, and, in most situations, have resulted in deleterious water activities in the treated preparations (e.g., water activities of 0.07 or higher). Microencapsulation and enteric coating techniques involve applying a film forming substance, usually by spraying substances contained in water, onto the dry probiotics. Water should not be used in a post drying treatment of probiotics since the water activity increase will cause a corresponding decrease in shelf-life. And even if the mixture is subsequently dried, the water activity may remain high, as it is extremely difficult to remove water from previously dry probiotics. A high water activity means that the probiotic manufacturer can only guarantee potency at time of manufacture, not at the time of consumption.